The present invention relates to a method of detecting phycocyanin-pigmented algae or bacteria (cyanobacteria) in water from reflected light. These organisms are generally referred to as phycocyanins and cyanobacteria.
In many instances it is desirable to be able to detect the presence microorganisms in water, particularly bodies of water that serve as a source for drinking water or that may serve as a site for recreation, such as for swimming boating, water sports and fishing. Many of these organisms in high concentrations can be harmful to the public and to the environment generally.
It is particularly desirable to be able to be able to detect the presence of microorganisms in water in a manner that is convenient and provides relatively immediate results so that the public may be warned or other actions taken to avoid or eliminate contamination of the assayed water.
The Laurentian Great Lakes have experienced toxin-producing blooms of the cyanobacterium Microcystis sp. on a number of occasions over the past decade, including a massive bloom in Lake Erie in 1995 that caused a variety of water quality problems and attracted broad public concerns (Taylor, 1997; Brittain et al, 2000; Budd et al, 2002).
Most freshwater systems in the world are affected by anthropogenic eutrophication, leading to undesirable increases in planktonic and benthic biomass. These phenomena often show large local differences and interactions with patterns of water flow. Among various problems, the amount and distribution of nuisance-forming cyanobacteria is of primary concern for water management. Cyanobacterial blooms may cause a variety of water quality problems, including dissolved oxygen depletion and subsequent fish kills, aesthetic nuisances (e.g., odors, scums, fish tainting, unsightliness), and unpalatable and possibly unsafe drinking water (Carmichael, 2001). Such problems can severely limit aquatic habitat, recreational activities, fisheries, and use of a water body as a potable water resource. Microcystis spp., a common bloom-forming species of cyanobacteria, was regularly documented in Lake Erie several decades ago, when the lake was heavily eutrophied as a result of anthropogenic activities (Makarewicz, 1993). Subsequent phosphorus abatement strategies initiated as part of the Great Lakes Water Quality Agreement have been largely successful resulting in a reduction in algal biomass and greater lake transparency. Despite these actions, blooms of Microcystis spp. have returned to Lake Erie, recurring each summer since 1995. The return of the blooms appears to coincide with the spread of invasive zebra mussels throughout Lake Erie and is possibly related to selective filtration of other phytoplankton by the mussels and rejection of Microcystis spp (Vanderploeg et al. 2001). During September, 1995, Lake Erie experienced a Microcystis spp. bloom resembling a thick slick of grass-green paint that extended over the entire surface of the western basin (Taylor, 1997; Brittain et al, 2000; Budd et al, 2002). Another notable bloom was reported in September, 1998 (Lake Erie LaMP, 2000). These blooms are of special concern because at least some Lake Erie strains of Microcystis spp. produce the peptide hepatotoxin microcystin, which is harmful to waterfowl or other animals that might drink the untreated water (Brittain et al, 2000). Microcystin has also been identified as a tumor promoter, making long-term ingestion of even low levels of the toxin of concern (Falconer and Humpage, 1996; Carmichael, 2001).
It would be of economic and public health value to be able to detect early stage (emergent) blooms of cyanobacteria, and Microcystis spp. in particular, especially if it is on a sufficiently timely basis for municipalities and recreation facilities to implement a response plan. It has been shown that remote sensing technology can be used to estimate the concentration and distribution of cyanobacteria through measuring the concentration of the pigment phycocyanin (Dekker, 1993), which is indicative of the presence of cyanobacteria. In waters off the southeastern coastal U.S. and the Gulf of Mexico, Subramaniam et al (2001) have applied a multispectral classification algorithm that employs data from the Sea-viewing Wide Field-of-View Sensor (SeaWiFS) for mapping blooms of Trichodesmium spp., a marine cyanobacterium. In cyanobacteria, phycobiliproteins constitute the major photosynthetic accessory pigments (MacColl and Guard-Friar, 1987). Whereas in marine species the pink-colored phycoerythrin is the dominant accessory pigment, in fresh water taxa, such as Microcystis spp., phycocyanin is the dominant pigment (MacColl and Guard-Friar, 1987). With the availability of LANDSAT 7 imagery for every 16-day overpass period, the present invention is intended to develop a LANDSAT TM algorithm for detecting various levels of phycocyanin in western Lake Erie. The present invention also allows for the mapping of turbidity in Lake Erie and its tributaries, to investigate relationships between phycocyanin and turbidity.
With the availability of LANDSAT Thematic Mapper (TM) imagery featuring an overpass cycle of every 16 days (8-day intervals, if both LANDSAT 5 and 7 are employed), one goal of the present invention was to develop a set of algorithms, methods of their use and devices for detecting cyanobacterial blooms in Lake Erie, based on a unique spectral signature produced by phycocyanin, a light-harvesting pigment complex ubiquitous among cyanophytes.
In addition to the features mentioned above, objects and advantages of the present invention will be readily apparent upon a reading of the following description and through practice of the present invention.